In the field of therapeutic ophthalmology, testing of visual performance plays an important role for obtaining an objective assessment when seeking to grasp the pathology of eye disease, make decisions regarding treatment strategy, verify the effect of treatment, and so forth. In general, visual performance subject to testing includes visual acuity, visual field, color perception, and other such measures of the performance with which visual information is input from the eye.
While testing of visual acuity is regularly carried out as an example of such visual performance, a broader definition of visual acuity would be the ability to recognize that a thing is present and to distinguish what it is (perception of form). This visual acuity (perception of form) is divided into four categories, these being “minimum perceptible acuity,” “minimum separable acuity,” “minimum legible acuity,” and “vernier acuity.” When measuring visual acuity, it is ordinarily “minimum separable acuity” that is measured.
To measure this “minimum separable acuity,” Landolt rings are typically used. A Landolt ring is of such shape that a notch is provided at a portion of a donut-like ring, minimum separable acuity being measured based on whether or not presence of this notch can be recognized. More specifically, a test subject is shown Landolt rings of differing size, and the size required for the test subject to be able to recognize the location of the notch is ascertained. Having done this, the size of the gap at the notch of the Landolt ring of the smallest size for which the location of the notch can be recognized can be taken to be the minimum separable acuity of the test subject.
Furthermore, testing of visual field is carried out to investigate any of a variety of diseases and/or the degree to which any of various respective diseases has progressed, such diseases including glaucoma, pigmentary degeneration of the retina, diabetic retinopathy, detachment of the retina, and macular degeneration. During such visual field testing, a perimeter is used to measure the range over which peripheral objects can be seen when one gazes on a single point. More specifically, the face is held stationary relative to the perimeter, and the test subject is asked to stare at a central mark displayed at a display area within the perimeter. While in this state, lights or the like are made to appear at the periphery of the display area, and the test subject is asked to sound a buzzer when he or she sees these lights. By investigating the locations at which the test subject can or cannot see lights in this fashion, the visual field, and gaps therein, are investigated (see http://medical-checkup.info/article/43671142.html and http://www.nichigan.or.jp/public/disease/ryokunai_ryokunai.jsp).